Datsun Roadster Forum-311s.org

Hi,

I've been having this somewhat annoying problem of a sticky high idle with my '69 1600. (By the way, I've really been enjoying both driving this car and learning about how it works and fixing the occaisional hiccup. Also, driving the car, what a blast!) These are the details:

When I turn the engine on the car idles fine. When I increase engine speed and then slowly release the throttle the engine will slow down but then stick at 2k to 3k rpm. If I snap the throttle (i.e. release it very quickly) this doesn't happen.

To try and fix this I took apart and cleaned the linkage. This done I reinstalled the linkage but left the two carbs decoupled (and unhooked from the throttle cable). The problem still happened with each carb individually. The throttle shaft would stop it's rotation a few degrees short of the idle stop and would just sit there. I was able to rotate it all the way to the idle stop by hand without very much effort though. With the engine off (but still warm) this problem didn't exist, the shafts rotate freely.

I suspected that this might be related to a leaking throttle shaft so I sprayed around the shafts with carb cleaner and observed no dip in the idle so I don't think that's what's happening. However, there is about .5 mm or less in side to side play of each throttle shaft.

While I had the linkage off of the front carb I thought that I'd try turning the car on and rotating the throttle shaft by hand (it rotated very smoothly and freely with the engine off). When I did this it immediately sucked all the way closed and was very difficult to rotate open. When it did it popped all the way to full open and was hard to close. The engine roared, this worried me, so I closed the throttle and turned off the car. I don't know if this is normal behavior or not.

When I searched the archives it seemed that other people had had these problems but no one knew what to make of it. So, has anyone figured it out? Does this sound familiar to anyone? Any suggestions? What do I do?

Sincerely,
Eric Corwin

There are several things that can cause a high idle.
vacum leaks
sticky chokes
hot throttle cable

Vacum leaks will cause a high idle. Sometimes the chokes or choke for one carb can stick on when you think you have the chokes off. Let's face it moving parts tend to get worn and they end up not lining up well any more. On my 66 I had to take the carbs apart and clean things up really well. I reseated the needles by loosening them up on the damper and slowly sliding them into the throttle body. Pulling it back out and retighten the set screw. Another thing that can cause a high idle is the throttle cable heating up and contracting just enough to give you a high idle. I think your problem lies with the chokes this time around as it sounds like you checked for leaks already.

Steve

I recently had a similar problem on 240Z. The problem was the fuel nozzle on the bottom of the carb was slightly corroded/gummed up.
I fixed it by pulling the nozzle out, cleaning it really good with some carb cleaner and when I reinstalled them I put a light coating of white lithium grease so it slid very easy in the bushing on the carb. Also cleaned the bushing with carb cleaner and a pipe cleaner when I had the piston and needle out. Hope this helps out.
Mark